A tray type Zirconium-Cobalt (ZrCo) tritium storage bed with an“in-bed”gas flowing calorimetry function has been developed for a self-assaying system in a tritium storage and delivery system of nuclear fusion facilities. The ZrCo bed is installed in a primary vessel. And 6 kW cable heaters are brazed in the bottom of each tray. He loop tubes are brazed on the top side of each plate, and 32 W simulation heaters are also installed along the He loop. To evaluate characteristics of the He circulation loop for tritium inventory measurement, the He loop gas temperature increase (△T) was measured by using the simulation heaters.